I have been playing this game for just over 3 months now. I absolutely love how this game is played. However, in my mere 3 months here I have already maxed out 2 achievements, along with being 1 level off a couple others. While this isn't "necessary" it does help motivation to spread out how you play. Connecting Cities, competitions, ads, etc.
My suggestion would be to add additional levels to the current max. For example: If the Max for Competitions was level 15 at 1,000 Competitions - it could go up to lvl 25 or higher with 10,000 Competitions. Something to strive for longer than a game. Once a game round is done; all you are left with are stats that few look at. This way you can strive for leveling up your account throughout all your play through and servers.
**Not sure how this would affect Career engines... Since this would be in the high end of each achievement, it shouldn't affect much.